Monochloroacetic acid (MCA), also known as chloroacetic acid, is an important organic compound in industrial chemistry. It is a colorless crystalline solid or white flakes with a chloroform-like odor. In this article, we will discuss the properties, production methods, and various applications of MCA.

Chemical Properties

Monochloroacetic Acid is a carboxylic acid derivative where one hydrogen atom is replaced by a chlorine atom. Its molecular formula is C2H2ClO2. Some key chemical properties of MCA include:

- Melting point: around 155°C

- Boiling point: around 240°C

- Soluble in water, alcohols, acetone, and ether

- Strongly acidic with a pKa of 2.86

- Stable under normal conditions but can decompose when heated to produce toxic gases like phosgene and hydrogen chloride

Production

The main industrial process for MCA production is the chlorination of acetaldehyde or glyoxal with chlorine gas. Specifically:

1. From Acetaldehyde

Acetaldehyde is reacted with chlorine gas in the presence of a catalyst (usually zinc chloride) at 150-200°C. The reaction produces MCA in nearly quantitative yields.

CH3CHO + Cl2 → CH2ClCOOH

2. From Glyoxal

Glyoxal undergoes catalytic chlorination with chlorine in the liquid phase at 80-100°C to yield MCA.

(CHO)2 + Cl2 → 2CH2ClCOOH

Both routes produce MCA in high purity of around 98%. The production can be carried out as a batch or continuous process. Global MCA production capacity is estimated to be over 500,000 tons per year.

Applications

Due to its acidity and reactivity of the chlorine substituent, MCA finds diverse applications in chemical synthesis and industry. Some major uses are:

Herbicides: MCA is used to produce several important herbicides like dichlorprop, mecoprop, and 2,4-D. These herbicides are effective against broad-leaved weeds in agriculture.

Pharmaceuticals: It is used as an intermediate in the production of certain antibiotics, corticosteroids, and anesthetics. Some drugs containing MCA are probenecid, triamterene, and fosinopril.

Surfactants: Reacting MCA with alcohols yields chloroacetates which act as surfactants or emulsifiers in detergents, cleaners, and other formulations.

Polymers: Polymericmaterials like cellulose ethers, dispersants, and flocculants utilizeMCA as a precursor. For example, in the production ofhydroxyethyl cellulose.

Metal Extractants: Complexation reactions ofMCA help in solvent extractionof metals like cobalt from ores. It formswater-soluble chelates facilitating separation.

Other Uses: Miscellaneous applications include as a delinting agent in cotton processing, flame retardant, plasticizer, ink component, tanning agent, and more.

Toxicity and Regulations

Being a chlorinated derivative, MCA is toxic and poses hazards to human health as well as the environment if not handled properly. Its vapor is irritating to eyes and respiratory tract. Regulatory bodies specify limits on occupational and environmental exposure. Proper waste disposal methods must be followed for safe use in industries.

Its leading production routes from acetaldehyde and glyoxal were explained along with major applications in herbicides, pharmaceuticals, polymers, and other areas. Safe handling is important considering its toxicity. MCA will continue to play an important role as a building block in fine and specialty chemicals production.